1. Field of the Invention
The present invention relates to a fine pattern forming apparatus for forming a fine pattern on a substrate or in a thin film formed on the substrate, and a method of forming the fine pattern.
2. Description of the Related Art
FIG. 1 is a schematic cross-sectional view of a conventional fine pattern forming apparatus, e.g., a plasma etching apparatus. In this apparatus, a semiconductor substrate 2, in which a fine pattern is to be formed, is disposed within a vacuum chamber 1. The semiconductor substrate 2 may be one which has on its surface a polycrystal-line silicon thin film and on the polycrystal-line silicon thin film a photoresist pattern serving as a mask which resists etching. In the vacuum chamber 1, the semiconductor substrate 2 is placed on a stage 4 which also serves as an electrode connected to a high-frequency power source 3 for supplying high-frequency power. An opposed electrode 6 with gas nozzles 5 provided therein to uniformly supply an etching gas which is a reactive gas, e.g., chlorine gas, toward the semiconductor substrate 2 is disposed in opposed relation to the semiconductor substrate 2. The vacuum chamber 1 is provided with an evacuation port 7 through which the vacuum chamber 1 is evacuated as well as a reactive gas supply port (not shown) through which the etching gas is supplied into the vacuum chamber 1. An opposed electrode 6 moving means 8 made of, for example, a screw is provided on the portion of the vacuum chamber 1 on which the opposed electrode 6 is mounted so as to provide a predetermined gap between the opposed electrode 6 and the stage 4.
The thus-arranged conventional fine pattern forming apparatus will be operated in the manner described below. First, an etching gas is introduced into the interior of the vacuum chamber 1 from the reactive gas supply port (not shown) through the gas nozzles 5 while the vacuum chamber 1 is evacuated from the evacuation port 7 by an evacuation means (not shown). Next, a high-frequency voltage is applied between the stage 4 and the opposed electrode 6 by the high-frequency power source 3 to generate a glow discharge, by means of which the etching gas introduced into the vacuum chamber 1 is activated and a plasma A is generated, thereby producing active neutral molecules, neutral atoms and ions. Etching of the semiconductor substrate 2 progresses due to the presence of these molecules, atoms and ions, and a fine pattern is thus formed.
The above conventional fine pattern forming techniques has the following drawbacks.
(1) Uniformity of the etch rate
In the conventional techniques, since the gap between the electrodes is fixed or changed mechanically, it is difficult to provide an optimum electrode gap which greatly affects uniformity of the etching. Furthermore, since spatial distribution of the activated halogen gas or ions occurs, when a fine pattern is to be formed on a sample having a large diameter, a non-uniform distribution of the etch rate across the diameter occurs. A reduction in the etch rate requires a large etching chamber.
(2) In the conventional techniques, since the stage 4 can be moved only mechanically, generation of dust caused by the movement cannot be eliminated. In consequence the performance of the apparatus is reduced, and the interior of the chamber 1 must be cleaned frequently. In particular, by-products of the etching gas, which may would be the cause of generation of dust by themselves, adhere to the moving means 8 for the opposed electrode 6 and peel off from the moving means 8 when the semiconductor substrate 2 is placed on or removed from the stage 4, generating dust.